This invention relates generally to the conversion of oxygenates to olefins, more particularly, to light olefins.
A major portion of the worldwide petrochemical industry is concerned with the production of light olefin materials and their subsequent use in the production of numerous important chemical products via polymerization, oligomerization, alkylation and the like well-known chemical reactions. Light olefins include ethylene, propylene and mixtures thereof. These light olefins are essential building blocks for the modern petrochemical and chemical industries. The major source for light olefins in present day refining is the steam cracking of petroleum feeds. For various reasons including geographical, economic, political and diminished supply considerations, the art has long sought a source other than petroleum for the massive quantities of raw materials that are needed to supply the demand for these light olefin materials.
The search for alternative materials for light olefin production has led to the use of oxygenates such as alcohols and, more particularly, to the use of methanol, ethanol, and higher alcohols or their derivatives such as dimethyl ether, diethyl ether, etc., for example. Molecular sieves such as microporous crystalline zeolite and non-zeolitic catalysts, particularly silicoaluminophosphates (SAPO), are known to promote the conversion of oxygenates to hydrocarbon mixtures, particularly hydrocarbon mixtures composed largely of light olefins.
The amounts of light olefins resulting from such processing can be further increased by reacting, i.e., cracking, heavier hydrocarbon products, particularly heavier olefins such as C4 and C5 olefins, to light olefins. For example, U.S. Pat. No. 5,914,433 to Marker, the entire disclosure of which is incorporated herein by reference, discloses a process for the production of light olefins comprising olefins having from 2 to 4 carbon atoms per molecule from an oxygenate feedstock. The process comprises passing the oxygenate feedstock to an oxygenate conversion zone containing a metal aluminophosphate catalyst to produce a light olefin stream. A propylene stream and/or mixed butylene is fractionated from said light olefin stream and cracked to enhance the yield of ethylene and propylene products. This combination of light olefin product and propylene and butylene cracking in a riser cracking zone or a separate cracking zone provides flexibility to the process which overcomes the equilibrium limitations of the aluminophosphate catalyst. In addition, the invention provides the advantage of extended catalyst life and greater catalyst stability in the oxygenate conversion zone.
While the integration of olefin cracking with oxygenate conversion can significantly improve the economics associated with such oxygenate conversion processing by upgrading the value of C4+ byproduct resulting from the oxygenate conversion reactor, further improvements such as relating to reducing or minimizing system processing costs and complexity are desired and are being sought.
In view thereof, there is a need and a demand for improved processing and systems for the conversion of oxygenates to olefins and, more particularly, for such processing and systems such as to result in an increase in the relative amount of light olefins.